The ability of x rays to penetrate through material has been exploited extensively, such as in non-invasive and non-destructive imaging in medical and industrial applications. One example is computed tomography (CT), which relies on rotating the sample while collecting multiple images, or projections, with an x-ray transmission imaging instrument. Using applicable tomography algorithms, including the filtered backprojection, algebraic reconstruction technique (generally abbreviated as ART) and its derivatives, or the Fourier inversion techniques, a three dimensional image of the sample can be generated.
One specific application is failure analysis of integrated circuits and their packaging. Here, the penetrating power of x rays with tens to hundreds of kilo electron-Volts (keV) energy provides the ability to image internal structures of the ICs. These x-ray inspection tools typically provide resolutions on the order of tens of micrometers to nanometers.
In these CT applications, control over the position of the sample rotation axis is important to ensure that the region of interest of the sample is located within the field of view of the x-ray transmission imaging device and remains within the field of view throughout the full rotation range. For x-ray microscope imaging instruments, it is desirable that the rotation of a sample be accurate to within tens of nanometers in all three dimensions. This allows a sample to be rotated in the x-ray beam with the volumetric region of interest maintained in the x-ray beam so that later tomographic reconstruction can possibly be performed with minimal or even without additional alignment procedures for the projections.